Composite structural reinforcement member

ABSTRACT

A reinforced structural member has a w-shaped reinforcement member that carries a thermally expandable resin-based material. The w-shaped reinforcement member is placed in the channel of a hollow structural member over a transverse pin which fits through the slot of the reinforcement member. The structural member is heated to expand the resin-based material which locks the reinforcement member in place, thereby significantly strengthening the structural member.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to automotive body structuralmembers and, more specifically, relates to reinforcement members forincreasing the strength of automotive body structural members.

BACKGROUND OF THE INVENTION

In a number of design applications, particularly in the automotiveindustry, it is essential to provide structural members which arelight-weight and yet which have high strength characteristics. A numberof exotic metal alloys and the like have been proposed by others in thepast for use in forming high strength structural members; however, insome applications, including in the automotive industry, the cost ofthese alloys is typically prohibitive. Accordingly, there is a need forstructural reinforcement members which are light-weight and low-cost andwhich can be used to compliment existing design structures.

There is a considerable body of prior art dealing with the reinforcementof motor vehicle structural components. In U.S. Pat. No. 4,901,500,entitled "Light-Weight Composite Beam," a reinforcing beam for a vehicledoor is disclosed which comprises an open channel-shaped metal memberhaving a longitudinal cavity which is filled with a thermosetting orthermoplastic resin-based material. In U.S. Pat. No. 4,908,930 entitled,"Method of Making a Torsion Bar," a hollow torsion bar reinforced with amixture of resin with filler is described. The tube is cut to length andcharged with a resin-based material.

In U.S. Pat. No. 4,751,249, entitled "Reinforcement Insert for aStructural Member and Method of Making and Using the Same," a precastreinforcement insert for structural members is provided which is formedof a plurality of pellets containing a thermosetting resin and a blowingagent. The precast is expanded and cured in place in the structuralmember. Also, in U.S. Pat. No. 4,978,562, entitled, "Composite TubularDoor Beam Reinforced with a Syntactic Foam Core Localized in the Midspanof the Tube," a composite door beam is described which has a resin-basedcore that occupies not more than one third of the bore of a metal tube.

In co-pending U.S. patent application Ser. No. 245,798 filed May 19,1994, entitled "Composite Laminate Beam for Automotive BodyConstruction," a hollow laminate beam characterized by highstiffness-to-mass ratio and having an outer portion which is separatedfrom an inner tube by a thin layer of structural foam is described.

Although in some applications, there are advantages to these prior artreinforcement techniques, there is a need to provide a reinforcement forrail sections which significantly increases the strength of the rail,particularly at stress points, in a manner which is not only low-cost,but also which adapts readily to mass production assembly.

In addition, it is known that cyanoguanidine is a commonly-used latentcuring agent for foamed epoxy polymers. The most frequently usedmaterial has a nominal particle size of about 80 microns. For higherreactivity, micronized versions are sometimes used, e.g. 90% ofparticles less than 30 microns. In the prior art, conventional usage ofcuring agents may cause "burning" of the foamed polymer. This is becausethe heat from the exothermal curing reaction does not readily dissipate.This solution is, however, not practical when the temperature of theoven is pre-set for other conditions, i.e., paint curing the like.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a reinforced structuralmember. The reinforced structural member has a longitudinal cavity inwhich a reinforcement member is disposed. The reinforcement memberincludes a slot through which a pin or other engagement means extends.The pin is secured to opposed sidewalls of the structural member. Thesides of the reinforcement member are open and the interior of thereinforcement member is filled with a resin-based material. Thereinforced structural member is assembled by securing the pin inposition and then dropping the reinforcement member which is filled withresin-based material over the pin. The open sides of the reinforcementmember and the resin-based material therein are adjacent sidewalls ofthe structural member, with the pin passing through the open slot of thereinforcement member. The structural member, which may comprise a motorvehicle rail, moves through a primer oven whereupon the resin-basedmaterial expands and adheres to the sidewalls of the structural memberto form a strong bond with the inner walls of the structural member. Theexpanded resin-based material effectively creates a single unitarystructure comprising the reinforcement member, the expanded resin andthe structural member.

In another aspect, openings in the reinforcement member adjacent thebottom of the structural member allow resin to expand through theopenings and bond to still another surface of the structural member toprovide even greater bonding of the reinforcement member to thestructural member.

In still another aspect, the present invention provides a novelepoxy-based reinforcement material which contains epoxy resin, anelastomer, a filler, fumed silica, high strength glass spheres, alongwith curing agent, an accelerator and a blowing agent.

In the present invention, the overall strength of the structural memberis significantly increased, reducing cracks at stress points where thereinforcement member is positioned.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a portion of a rail member reinforced inaccordance with the present invention.

FIG. 2 is a side elevational view of the rail member of FIG. 1 partiallybroken away to illustrate the placement of the reinforcement member andtransverse pin.

FIG. 3 is a perspective view of the structural reinforcement carriermember before insertion into the hollow structural member of FIGS. 1 and2.

FIG. 4 is a cross-section along lines 4--4 of FIG. 3.

FIG. 5 is a perspective view of the hollow structural member withtransverse reinforcement pin prior to insertion of the reinforcementmember.

FIG. 6 is a side elevational view of a hollow frame section partiallybroken away and reinforced in accordance with the present invention inanother embodiment.

FIG. 7 is a cross-section of the reinforcement member of FIG. 6 alonglines 7--7.

FIG. 8 is a perspective view of the reinforcement member of FIG. 3without the resin-based core.

FIG. 9 is an elevational view of a reinforcement member in anotherconfiguration for use in the present invention.

FIG. 10 is an elevational view of a reinforcement member and retainingpin in another configuration for use in the present invention.

FIG. 11 is a plan view of the structure shown in FIG. 1, but with theresin-based core removed.

FIG. 12 is an elevational view of a reinforcement member in anotherconfiguration for use in the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1 of the drawings, reinforced structure 18 is seenhaving hollow structural member 20 with top or closure plate 22 (shownin phantom). Structural member 20 has opposed sidewalls 24 and 26 andfloor or bottom surface 28 and is thus in the nature of a channel-shapedmember. Rod or pin 30 extends between opposed sidewalls 24 and 26 asbest shown in FIG. 5 of the drawings. Pin 30 serves as a shock absorberattachment and as a retaining member for reinforcement member 32.Reinforcement member 32 is disposed within longitudinal channel orcavity 34 of hollow structural member 20 and has a carrier portion 33(best shown in FIG. 8) which serves as a carrier or container forresin-based reinforcement/bonding material 36. In FIG. 2 of thedrawings, sidewall 24 is shown partially broken away to revealreinforcement member 32 and the end of pin 30.

Hollow structural member 20 is preferably formed of metal, for examplesteel, and is most preferably a rail of a motor vehicle. Accordingly, inthe most preferred embodiment, reinforced structural member 18 is anautomotive beam or rail.

Referring now to FIGS. 3, 4 and 8 of the drawings, carrier 33 hasexternal sidewalls 38 and 40, internal sidewalls 42 and 44, lower walls46 and 48 and a connecting wall 50 such that two channel-shaped cavitiesor reservoirs 52 and 54 are defined. As best shown in FIGS. 4 and 8,these walls define a c-shaped resin receiving cavity 56. In thisfashion, resin-based reinforcement/bonding material 36 forms a c-shapedresin body structure or core 58.

It is to be understood that a number of geometries may be suitable foruse as carrier 33 and that the w-design or configuration, whilepreferred, is only one such configuration. For example a corrugatedconfiguration 70 as shown in FIG. 9 or an inverted u-shaped structure 72as shown in FIG. 10 having an external coating of resin-based material(i.e. no external sidewalls) may be suitable in a given application.Also, it may be suitable to completely eliminate carrier 33 and utilizea free-standing resin body 74 as shown in FIG. 12. It is generallysufficient that reinforcement member 32 have means for containing orsupporting a resin-based reinforcing body and means for interfacing witha position-locating retention means such as pin 30. Most preferably,carrier 33 will define one or more containment sites or reservoirs forthe resin-based reinforcing/bonding material while still having openingssuch that the resin-based reinforcement/bonding material may expand andbond with sidewalls 24 and 26 of hollow structural member 20.

The gauge or thickness of carrier 33 may vary, but is typically between0.025 and about 0.060. The dimensions of reinforcement member 32 shouldclosely match channel 34 so that there are at least some points ofcontact between carrier 33 and sidewalls 24 and 26, but should notrequire that channel 34 be expanded for insertion of reinforcementmember 32 during assembly. Pin 30 is preferably metal and, as stated,serves to retain reinforcement member 32 in place by engagement withslot 60 defined by internal sidewalls 42, 44 and connecting wall 50 ofcarrier 33. It is most preferred that any clearance between pin 30 andslot 60 be sufficiently small such that reinforcement member 32 does notmove significantly even prior to expansion of resin-basedreinforcement/bonding material 36. The composition of resin-basedreinforcement/bonding material 36 as well as the method of assembly ofreinforced structural member 18 will be described more fully below.

In still another embodiment of the present invention, referring now toFIGS. 6 and 7 of the drawings, reinforcement member 32' is shown havinga plurality of openings or channels 62 through which resin-basedmaterial 36' flows during expansion in the assembly process. This formsadditional bonding regions 64 on floor surface 28' of hollow structuralmember 20. By providing openings 62 in this manner, additional bondingand reinforcing strength is obtained for reinforced structure 18. Inthis embodiment, all other features of reinforced structural member 18are identical to those described in connection with the embodiment shownin FIGS. 1 through 5.

A number of materials may be suitable for use in forming resin-basedreinforcement/bonding material 36. Suitable materials should havesufficient body when uncured or partially cured so that the materialdoes not significantly flow out of carrier 33 once formed and prior toinserting in channel 34. Thus, it will be appreciated that carrier 33receives resin-based reinforcement/bonding material 36 in a preparatorystep to form a unit which is subsequently dropped into channel 34. Inaddition to having sufficient body, it is important that resin-basedreinforcement/bonding material 36 permanently expand to contactsidewalls 24 and 26 (and floor surface 28 in the embodiment shown inFIGS. 6 and FIG. 7) and this permanent expansion provides the desiredcompressive strength. It is also important that resin-basedreinforcement/bonding material 36 adhere strongly to the inner surfacesof carrier 33 as well as to sidewalls 24 and 26. Resin-basedreinforcement/bonding material 36 must also be sufficiently thermallystable such that it does not degrade at the temperatures experienced inpaint curing ovens and the like. Resin-based reinforcement/bondingmaterial 36 should also be light-weight and low-cost and, in general,should impart excellent mechanical strength to reinforced structuralmember 18.

More specifically, resin-based reinforcement/bonding material 36 shouldhave a density of from about 35 pounds per cubic feet to about 65 poundsper cubic feet prior to being fully cured and from about 25 pounds percubic feet to 45 pounds per cubic feet once fully expanded in place. Thecompressive strength of resin body 58 (after expansion and curing)should be at least 1,000 pounds per square inch and more preferablyabout 1,500 pounds per square inch or greater. The bond between resinbody 58 and sidewalls 24 and 26, where sidewalls 24 and 26 are steel,should be sufficient to maintain the intensity of the metal/cure bond.This minimizes separation of resin body 58 from sidewalls 24 and 26 aswell as from carrier 33. Cured resin body 58 should be able to withstandtemperatures in excess of 450° F. for short times absent any significantapplied stress and temperatures up to about 175° F. for extended periodswithout exhibiting substantial heat induced distortion or segregation.

Resin body 58 may be formed in place in carrier 33 by closing the opensidewalls 39 and 41 of carrier 33 and injecting or pouring a liquid orpaste like resin-based material therein. Material 36 may then behardened in place by curing or cooling. Alternatively, resin body 58 maybe preformed and then inserted into resin receiving cavity 56 which isdefined by carrier 33.

One preferred material for use as resin-based reinforcement/bondingmaterial 36 includes a synthetic resin, an expandable self-foamingagent, and a filler. All percentages herein are by weight unlessotherwise indicated. In one embodiment, synthetic resin comprises fromabout 45% to about 70% by weight, and preferably from about 50% to about60% by weight of resin body 58. A cellular structure is most preferredsince it provides a low density, high strength material which is strongand yet light-weight. The self-foaming agent may comprise a chemicalblowing agent such as azodicarbonamide or P, P'-oxybis (benzene sulfonylhydrazide) which comprises from about 0.1% to about 10% and morepreferably from about 0.5% to about 2% by weight of resin body 58. Inaddition, in some applications it may be preferable to use plasticmicrospheres which may be either thermosetting or thermoplastic andwhich are in their unexpanded state until reinforced structural memberis heated to expand material 36. It is to be understood that material 36is not fully expanded until after reinforcement 32 is in position inchannel 34. Where blowing agents are utilized as a self-foaming agent,they comprise from about 0% to about 10% and more preferably from about1.5% to about 3% by weight of resin body 58. A number of fillers aresuitable, including glass or plastic microspheres, fumed silica, calciumcarbonate, milled glass fiber and chopped glass strand. A fillercomprises from about 20% to about 50% by weight and more preferably fromabout 25% to about 40% by weight of resin body 58.

Preferred synthetic resins for use in the present invention includethermosets such as one-part epoxy resins, vinyl ester resins, thermosetpolyester resins, and urethane resins. The average molecular weight(number average) of the resin component is from about 1,000 to about5,000,000. Where the resin component of the material 36 is athermosetting resin, various accelerators such as modified ureas andborontrichloride are included. A curing agent such as dicyandiamide isused to cure the resin. A functional amount of accelerator is typicallyfrom about 0.1% to about 5% of the resin weight with a correspondingreduction in one of the three components, resin, self-foaming agent orfiller. Some thermoplastics may also be suitable.

A most preferred composition for use as material 36, and one whichcomprises another aspect of the present invention, is an uncuredone-part epoxy system which is provided in the form of a high-viscosity"dough" that is placed in carrier 33 as described above. With thepreferred one-part epoxy dough, the uncured material 36 and thus,reinforcement member 32 can be washed, phosphated or otherwise treatedwith alkaline or acidic solution without noticeable deterioration ofmaterial 36. Thus, material 36 in this embodiment is resistant to acidsand bases in its uncured state. Particularly in automobile applications,this feature allows reinforcement member 32 to be inserted at an earlystage in the production line.

Accordingly, in one preferred embodiment, material 36 contains in weightpercent, from about 30% to 70% epoxy resin, from about 0% to 20%elastomers such as polybutyl rubber, acrylonitrilebutadiene rubber (ABR)or polyisoprene, from about 1% to 30% filler such as calcium carbonate,fumed silica, high strength glass microspheres and from about 0% to 10%blowing agent such as azodicarbonamide or P, P'-oxybis (benzene sulfonylhydrazide).

In addition, material 36 further includes from about 2% to 10% curingagent such as dicyandiamide or cyanoguanidine. It has been discoveredthat the size of the particulate curing agent is an important feature ofthe preferred formulation of material 36. By providing a powdered orparticulate curing agent wherein 40% of the particles are greater than15 microns in diameter, which is fully blended with the otherconstituents of material 36, even curing with no thermal degradation maybe obtained at the temperatures experienced in automotive priming ovens.In other words, by utilizing a one-part epoxy resin containing blends ofcyanoguanidine which have a high coarse particle content, no "burning"or reduced levels of "burning" of the interior of the cured epoxy foammass.

From about 0% to 5% accelerator, such as modified ureas orborontrichloride is also preferably included in material 36. From about0% to 10% carbon black may also be included.

In the most preferred embodiment, material 36 includes from about 1% to6% hydrophobic silica and from about 18 to 27 high strength glassspheres which range from about 20 microns to about 400 microns indiameter. The high strength spheres should have a hardness (crushresistance) of at least 500 psi.

The most preferred epoxy resins are solid bisphenol A and solidbisphenol F including liquid epoxy resin. One such epoxy resin is soldas DGEBPA resin by The Peninsula Polymer Company.

The most preferred elastomer is acrylonitrile-butadiene rubber which issold as NIPOL 1312 by The Zeon Company of Kentucky.

A preferred filler is stearic acid treated calcium carbonate sold asWINNOFIL SPT by The Zeneca Company of Massachusetts.

The preferred fumed silica are sold as CAB-O-SIL TS 720 by The CabotCompany if Illinois.

The preferred high strength glass spheres are sold as B38 Glass Bubblesby The 3M Company of Minnesota.

The most preferred curing agent, cure accelerator and blowing agent aresold as Dicyandimine G sold by SKW of Georgia, AMICURE UR (Air ProductsCompany of Pennsylvania) and CELOGEN OT (Uniroyal Company ofConnecticut, respectively.

In the most preferred embodiment, the preparatory material (uncured) 36,should have a dough-like consistency. Material 36 can be prepared byconventional techniques such as mixing the various components together.

In the following table, a preferred formulation for resin-basedreinforcement/bonding material 36 is set forth. It is to be understoodthat this formulation is merely preferred and that other formulationsmay be suitable in a particular application.

                  TABLE I                                                         ______________________________________                                                          WT. %                                                       ______________________________________                                        Epoxy Resin         50.45                                                     Acrylonitrile-Butadiene Rubber                                                                    4.33                                                      Calcium Carbonate   5.81                                                      Carbon Black        0.13                                                      Fumed Silica        3.55                                                      High Strength Glass Spheres                                                                       22.40                                                     Curing Agent        4.33                                                      Accelerator         1.29                                                      Blowing Agent       0.71                                                      ______________________________________                                    

For assembly of reinforced structural member 18, and referring now toFIGS. 1 and 3 of the drawings, resin-based reinforcement/bondingmaterial 36 is prepared and placed in carrier 33 as previouslydescribed. A number of filled reinforcement members 32 may be preparedat one time and stored for future use. It is to be understood that atthe point of time when reinforcement member 32 is to be dropped intochannel 34, resin-based reinforcement/bonding material 36 is of a highviscosity such that it is retained within reinforcement member 32, butit is still capable of expanding and fully curing or solidifying to forma rigid structure (resin body 58) in channel 34 in combination withcarrier 33. Bores are drilled through sidewalls 24 and 26 and pin 30 isinserted therein. It will be appreciated that the function of pin 30 isto retain reinforcement member 32 in place in channel 34 and that othersecuring means such as nubs or the like extending only partially fromeach opposed sidewall 24 and 26 may be suitable or desirable in anygiven application. Other retaining means may also be suitable.Preferably, pin 30 is welded in place such that it extends acrosschannel 34 as best shown in FIG. 5 and provides strength to structure18.

Reinforcement member 32 is dropped into channel 34 such that pin 30slides into slot 60 thereby securing reinforcement member 32 in place(i.e. reinforcement member 32 is restrained from movement longitudinallyalong channel 34). In the embodiment shown in FIG. 1, top plate 22 isthen placed on hollow structural member 20 and welded in place such thatchannel 34 is completely closed. As the motor vehicle moves through apaint oven, resin-based reinforcement/bonding material 36 thermallyexpands to form rigid resin body 58 which, as stated, locksreinforcement member 32 in channel 34. In other words, once expanded andfully solidified or cured, reinforcement member 32, resin body 58 andopposed walls 24 and 26 form an integral mass of material that addssignificant strength to reinforced structural member 18. Although thetime and temperatures may vary considerably depending upon the choice ofmaterials used to form resin-based reinforcement/bonding material 36,with the preferred formulations set forth in the foregoing tables,material 36 should be heated to a high enough temperature, dependingupon the amount of accelerator, cure agent, and mass.

Reinforced structure 18 has a number of advantages over prior artstructures. By strategic placement of reinforcement member 32 at stresspoints, metal fatigue and cracking may be reduced without the use ofheavy gauge metals to form structural member 20. Thus, it is preferredthat carrier 32 occupies less than one-half the volume of structure 20,i.e., of cavity 34. It will be appreciated also that the preferredconfiguration of carrier 33 results in the formation of a series (threein the preferred w-shaped design) of u-shaped or column-shapedstructures that extend between sidewalls 24 and 26. Resistance tocompressive forces and torque of pin along an axis through sidewalls 24and 26 and thus along the length of the columns is significant.

It will be appreciated that carrier 33 acts as a container for resinbody 58 which keeps the body 58 from bulging, cracking and spalling, aswell as acting as a handling mechanism. This is particularly importantwhere resin body 58 is the primary load bearing unit. In turn, resinbody 58 stabilizes carrier 33 such that carrier 33 does not buckle priorto the time resin body 33 acts as a support structure.

While a particular embodiment of this invention is shown and describedherein, it will be understood that the invention is not to be limitedthereto since many modifications may be made, particularly by thoseskilled in the art, in light of this disclosure. It is contemplatedtherefore that the present invention cover any such modifications asdoes fall within the true spirit and scope of this invention.

What is claimed is:
 1. A reinforced structural member, comprising:astructural member defining a space; a reinforcing member disposed insaid space, said reinforcing member having a carrier portion and athermally expanded portion, wherein said carrier portion is a carrierfor said thermally expanded portion, and said thermally expanded portionis bonded to said structural member and to said carrier portion; andmeans for retaining said reinforcing member in said structural member,wherein said carrier portion has at least one aperture through which aportion of said thermally expanded portion extends, said extendedportion of said thermally expanded portion being bonded to saidstructural member.
 2. A reinforced structural member, comprising:astructural member defining a space; a reinforcing member disposed insaid space, said reinforcing member having a carrier portion and athermally expanded portion, wherein said carrier portion is a carrierfor said thermally expanded portion, and said thermally expanded portionis bonded to said structural member and to said carrier portion; andmeans for retaining said reinforcing member in said structural member,wherein said carrier portion defines a slot and wherein said retainingmeans includes a projection attached to said structural member andprojecting into said space, said projection being at least partiallydisposed in said slot to retain said reinforcing member in said space.3. A reinforced structural member, comprising:a structural memberdefining a space; a reinforcing member disposed in said space saidreinforcing member having a carrier portion and a thermally expandedportion, wherein said carrier portion is a carrier for said thermallyexpanded portion, and said thermally expanded portion is bonded to saidstructural member and to said carrier portion; and means for retainingsaid reinforcing member in said structural member, wherein saidthermally expanded portion is a resin-based material.
 4. A reinforcedstructural member, comprising:a structural member defining a space; areinforcing member disposed in said space, said reinforcing memberhaving a carrier portion and a thermally expanded portion, wherein saidcarrier portion is a carrier for said thermally expanded portion, andsaid thermally expanded portion is bonded to said structural member andto said carrier portion; and means for retaining said reinforcing memberin said structural member, wherein said structural member is a metalrail section, said carrier portion has a geometry which defines both aslot and at least one reservoir, said thermally expanded portion is aresin-based material disposed in said reservoir, said retaining means isa projection extending into said space and attached to said structuralmember, said projection extending into said slot to retain saidstructural member in said space.
 5. The invention recited in claim 4,wherein said carrier portion is a w-shaped metal sheet having tworeservoir portions, one of said reservoir portions being disposed on onesaid of said slot and the other of said reservoir portions beingdisposed on the other side of said slot, said thermally expanded portionbeing disposed in both of said reservoirs.
 6. The invention recited inclaim 4, wherein said w-shaped metal sheet has a longitudinal axispassing through both of said reservoirs and a transverse axisperpendicular to said longitudinal axis, and wherein said slot is achannel extending along said transverse axis, said structural memberhaving opposed side walls, and said w-shaped metal sheet being disposedin said space with said transverse axis extending from one of saidopposed side walls to the other of said opposed sidewall.
 7. Areinforced structural member, comprising:a steel rail having opposedside walls and defining a longitudinal channel, said longitudinalchannel lying along a longitudinal axis; disposed in said channel acavity-defining resin supporting reinforcement member formed of metaldisposed in said channel, said resin supporting reinforcement memberhaving at least one column-shaped structure and at least one slot, saidcolumn-shaped structure having a column axis along the length of thecolumn-shaped structure, said column axis extending between said opposedside walls perpendicular to said longitudinal axis; a pin attached tosaid steel rail and extending into said slot; and a resin-based coredisposed in a cavity defined by said cavity-defining resin supportingreinforcement member, said resin-based core being adhered to saidsidewall and to said cavity defining resin supporting reinforcementmember.
 8. The invention recited in claim 7, wherein said resin-basedcore is formed of a thermally expanded resin-based material.
 9. Theinvention recited in claim 7, wherein said cavity defining resinsupporting reinforcement member has a w-shaped configuration whichdefines three column-shaped structures.
 10. A reinforced structuralmember, comprising:a structural member defining a space; a reinforcingmember disposed in said space, said reinforcing member consistingessentially of a thermally expanded resin-based body bonded to saidstructural member, said resin-based body further defining a slot; andmeans for retaining said reinforcing member in said structural member,said retaining means including means for engagement in said slot. 11.The invention recited in claim 10, wherein said retaining means is a pinsecured to said structural member.
 12. A method for reinforcing astructural member comprising the steps of:forming a metal carrier, saidmetal carrier defining a resin-receiving space and a slot; applying anexpandable resin-based material to said carrier at said resin receivingspace; providing a hollow structural member having a longitudinal cavityand securing a pin to said hollow structural member in said cavity;positioning said metal carrier with said resin-based material thereon insaid cavity with said pin passing through said slot; and expanding saidresin-based material to bond said carrier to said structural member. 13.The invention recited in claim 12, wherein said expandable resin-basedmaterial is thermally expanded and wherein said expansion step iscarried out by heating said structural member.
 14. A reinforced rail fora motor vehicle, comprising:a hollow rail section having opposedsidewall defining a longitudinal channel; a pin having one end attachedto one of said sidewall and another end attached to the other of saidsidewall; a w-shaped metal strip defining two reservoirs and a slot; athermally expanded resin-based core bonded to said w-shaped metalcarrier in said reservoirs; said w-shaped metal strip being positionedin said hollow rail section between said opposed sidewall and beingbonded to said sidewalls by said resin-based core; and said pin beingposition in said slot.
 15. The invention recited in claim 14, whereinsaid rail has a lower wall connecting said opposed sidewall and saidw-shaped metal strip has at least one aperture therein through which aportion of said resin-based core extends, said extended portion of saidcore being bonded to said floor.